A Constant Surprise
by dharmamonkey
Summary: Hodgins and Zack are struggling with the design for their water balloon catapult and end up getting help from an unexpected source.


**A Constant Surprise**

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**By**: dharmamonkey

**Rated**: K+

**Disclaimer**: _I don't own jack. However, I am definitely interested in renting Booth. A five-hour minimum would apply. _

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**A/N: **_This story is part of the Bones Fanfic Secret Santa and is my top-secret commando gift to _**bangelforeverandalways **_who had a pair of Zack/Hodgins scenarios on her list which I ended up combining in a twisted monkey kind of way. I hope you like it, kiddo. This scene is set sometime during early Season 2._

_Props to mathlady extraordinaire _**threesquares **_for her very helpful input._

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"I don't understand why our test scenarios didn't play out the way the models did," Zack Addy complained, gently tapping his fingers on the keyboard as he watched the computer-generated animation on the screen. "The variables were all—"

"Zack," Jack Hodgins said in a slightly chastising tone. "That's why we call them experiments. They don't always turn out quite the way you think they will. It's okay, though. We'll figure it out. We've got a few more days to get it right before—"

"We don't have a few more days," a loud, deep voice pierced the quiet of Hodgins' office. Startled, the two scientists looked up and saw the tall, broad-shouldered frame of Special Agent Seeley Booth standing in the doorway. "We need to get that cause of death nailed down pronto before our lead suspect pops smoke, flies the coop and ends up in Timbuktu."

Zack gave the intimidating agent a crooked-browed look. "Pop smoke?" he asked, puzzled by the reference. "The experiment in which Dr. Hodgins and I were engaged does not utilize smoke in any way. And why would the suspect abscond to Mali?"

Hodgins glanced at the young doctoral candidate and rolled his eyes, then looked back to Booth. "I'm waiting for the mass spec results to come in," he explained. "Should only be another ten or fifteen minutes, Booth."

Booth's brow furrowed momentarily then his rigid jaw softened somewhat. "What about cause of death?" he asked. "You got anything on that?"

"Yes, Agent Booth," Zack replied. "X-rays and micrographs confirmed my and Dr. Brennan's initial conclusions based on our visual assessment. Tristan Eckert died of blunt force trauma to the occipital bone along the lambdoid suture caused by a heavy, sharp, tapered object. Dr. Hodgins' mass spec results should be able to confirm the nature of the material based on smears of the metal left on the fragments of the cranium."

"In English, please," Booth grumbled, turning to Hodgins for a translation.

"He was hit in the back of the head, probably with a crowbar," the curly-locked scientist explained. "I'm running the microscopic particulates through the mass spec to confirm the metal and coating types so we can hopefully identify the crowbar by brand."

"Great," Booth said, tapping his foot impatiently as he glanced at his watch. "So what are you guys doing right now, then?"

Zack and Hodgins exchanged a knowing look and, after a moment of silent pause that made Booth arch a deeply suspicious eyebrow, Hodgins gave the younger scientist a slight upward nod of his chin.

"Dr. Hodgins and I are trying to figure out why our water balloon catapult design is not performing as expected," Zack explained.

Booth burst out laughing. "What?" he snorted. "You gotta be kiddin' me. This is what the American taxpayers are paying you two chuckleheads to work on? Does Cam know you're using her fancy lab equipment to design a..." He had to swallow a laugh. "A water balloon catapult?"

"She's the one who asked us to do it," Hodgins said vaguely. Booth's eyes narrowed as he finally pushed away from the door frame and walked into the office. "The Jeffersonian has an employee picnic every year and this year there's a water balloon catapult competition. Cam asked Zack and I to represent the Medico-Legal Lab."

Booth reached up and scratched the back of his head. He walked over and stood behind Zack as the young man restarted the computer animation. The agent's face took on a serious mien, his eyes narrowed and his lips pursed as his irises shifted from side to side while the CGI water balloon arced across the screen.

"Your model's totally wrong," he said flatly.

"What do you mean it's totally wrong?" Zack retorted defensively.

Booth's right eye narrowed briefly as he watched the animation cycle again. "Look," he said, pointing to the red cartoon balloon on the screen. "The shape of your projectile is off. For one thing, I doubt it's even really shaped that way unless you guys are using some wacky balloons, and in any case, if it is, then that shape is going to cause all kinds of problems after its discharged from the catapult." He watched the animation one more time and turned to Zach. "You haven't properly accounted for the way the shape will make it wobble, especially in the latter part of the trajectory when it's losing energy. I'd recommend using a more inflated balloon if you can and recalculating the parabolic trajectory on that..." Booth's voice suddenly trailed off. "What?"

Zach and Hodgins stared at the dark-eyed agent with open-mouthed shock.

Hodgins laughed. "It's just, uhh, well," he coughed. "I didn't think you were that well-versed in trigonometry, Booth."

The agent's brows knit in irritation. "I'm not," he said. "But I know enough about indirect fire techniques to know—"

"Indirect fire?" Zack interrupted him. "So what are you saying, Agent Booth?"

Booth snickered. "Your math is wrong, kid," he said, basking in the once-in-a-lifetime opportunity to tell two squints they bungled their math.

A smirk cut across Hodgins' lips. "Ahhh," he murmured knowingly. "_Riiiiight_..."

"What's going on?" Zack asked, his expression shaded in confusion.

Hodgins winked at Booth and then looked at Zack. "Booth was a sniper."

"Yeah," the younger scientist said, raising a nonplussed eyebrow. "So?"

The bug-and-slime guy grinned. "Long-distance sharpshooting is a form of indirect fire," he said.

"I have no idea what that means," Zack said, an edge of frustrated petulance to his voice.

Booth cleared his throat before Hodgins could launch into an exposition of one of his conspiracy theories. "_Direct_ fire is line-of-sight," the agent explained. "Like a pistol or other close-range firearm. Point and shoot. You aim, put the sights over the target, pull the trigger, then _bam_."

Zack quirked a curious eyebrow as he listened.

"But _indirect _fire is not line-of-sight," Booth continued. "The round follows an arc-like trajectory. Artillery and mortars are indirect fire weapons. So are catapults. And so are sniper shots longer than 200 meters."

Seeing the vaguely perplexed look in the other men's faces, he shrugged with a cocky flash of his dark eyebrows, then his expression quickly darkened as his gaze became more distant and unfocused.

"Even a high-velocity round like a large-caliber sniper's bullet will sink as it travels downrange and slows down," Booth said, drawing an arc with his hand in the air. "So you have to aim above the target. The farther downrange the target is, the higher you have to aim to be able to drop that round where you want it to go. A .308 round with a standard-issue 150 grain load will drop 6.7 inches over the course of 300 meters. At 1,000 meters, you have to account for 129 inches, again assuming a standard 7.62mm, 150 grain round. So at 1,000 meters, you're aiming more than ten feet above the target."

"It's all physics," Hodgins said. "And trigonometry."

Booth nodded. "Figuring out where to aim—yeah, that's just fancy math," he said casually. "We used tables that had all the basic math already plugged in, and we were taught at Sniper School how to adjust for wind, humidity, altitude, air density. The aiming was all math. Putting it where you wanted it..." His voice suddenly darkened again. "That's an art. A skill."

Several long moments of silence passed between the three men. Finally, Zack broke the silence.

"So we need to redo our calculations," he said. "Once we reconfirm the parameters of the projectile."

"Everything keys off that," Booth said wisely. After second, he pursed his lips and added, "Aside from sidewinds, which you can't anticipate right now anyway, if you can nail down the size and shape of your balloon and the volume/weight of the water that's gonna fill it, you should be golden. I'm sure you two brainiacs will destroy the competition."

Zack smiled, visibly proud to hear a rare compliment from the agent.

"Did you enjoy math in school, Agent Booth?" he asked.

Booth laughed and waved his hand. "God no," he said. "Hated it. Only kept up with it in school because I needed to so I could stay academically eligible to play basketball." He swallowed, then said, "In the Army, I became a sniper because I was a good shot, intuitively, I guess. The math was a necessarily evil."

The irony of his statement gave him pause as he bit the inside of his lip. Shrugging away a memory, he turned to Hodgins with a forced grin.

"So," he said with an encouraging waggle of his brow. "Show me your catapult..."

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**A/N**:_ Soooo..._

_I hope you all (especially holiday giftee_ **bangelforeverandalways**) _enjoyed that one. A bit different than my usual offering. ("That's right, people—I'm a constant surprise.") Who knew math could be so useful? _

_Since I'm not a psychic like Avalon, I'd love to know what you all thought. Please, please leave a review. Pretty please? *works the puppy dog eyes* _

_Thanks!_


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